The possibility of industrial applications of spintronics has been focused since the mid-1990s. Herein, the spintronics denotes a compound word of “spin and electronics”. That is, electronics research into techniques using “electric charge”, one of two characteristics of an electron, has been mainly conducted. However, current electronics research has been conducted to develop devices having new functions by using “spin”, i.e., the other characteristics of the electron.
The best way to utilize the spin of an electron is using a ferromagnetic material. In particular, magnetic tunnel junction (MTJ) device using a tunneling magnetoresistance (TMR) structure recently has received more attention due to its wide application areas.
Herein, the TMR structure denotes a structure of ferromagnetic material-insulating layer-ferromagnetic material, wherein the MJT device may be used as a means to store data by using an effect in which a tunneling current attributed to quantum mechanics is affected by a magnetization direction of a ferromagnetic material. Herein, the principle of being able to be used as the data storage means is due to magneto-resistance characteristics, wherein the magneto-resistance characteristics denotes characteristics in which resistance changes according to the arrangement of two ferromagnetic materials.
That is, in the case that magnetization directions of the two ferromagnetic materials are parallel, the tunneling current is the maximum, and in the case in which the magnetization directions of the two ferromagnetic materials are antiparallel, the tunneling current is the minimum. Ferromagnetic materials may have different electron densities depending on a spin direction.
When electrons at the Fermi level of the ferromagnetic material pass through the insulating layer, the electrons may easily move because possible spin directions of two ferromagnetic materials are coincide if the second ferromagnetic material is magnetized in the same direction as the first ferromagnetic material. However, if the ferromagnetic materials are magnetized in opposite directions, scattering of tunneling electrons occurs, and thus, resistance may be increased.
In this case, a material that may provide a high magnetoresistance (MR) ratio may be selected as a tunneling insulating layer, in which MgO has received attention as a new insulating layer.
Also, the uniformity of magnetoresistance as well as the high MR ratio is an important factor in determining the characteristics of a magnetic tunnel junction device. For this purpose, it is important to form a thickness of each layer uniformly, and particularly, it is important to form the thickness of the tunnel insulating layer evenly during a heat treatment process.
However, with respect to a typical magnetic tunnel junction device, many limitations in the uniformity of magnetoresistance have been reported. That is, the flatness of the tunnel insulating layer may be deteriorated due to a lower structure of the tunnel insulating layer during the heat treatment process.
The heat treatment process is an essential process for improving the characteristics of magnetic materials by crystallization of the tunnel insulating layer and the ferromagnetic materials. However, since the lower structure may become rough as the lower structure of the tunnel insulating layer is crystallized, the tunnel insulating layer formed on the lower structure is affected thereby, and thus, the flatness of the tunnel insulating layer deteriorates. As a result, according to a typical structure, since the characteristics of each magnetic tunnel junction device may be different even in the case in which each magnetic tunnel junction device is formed on the same wafer, the uniformity of magnetoresistance may not be secured.
Also, in a typical magnetic tunnel junction device, the tunnel insulating layer may be contaminated by the lower structure during the heat treatment process. In particular, for example, with respect to PtMn or IrMn which is used as a material of an antiferromagnetic (AFM) layer, manganese (Mn) particles may be disposed at an interface of the tunnel insulating layer while the Mn particles diffuse toward the tunnel insulating layer during the heat treatment process, and thus, the Mn particles may contaminate the tunnel insulating layer. In this case, the flatness of the tunnel insulating layer may deteriorate and as a result, it may adversely affect the uniformity of magnetoresistance.
Therefore, a magnetic tunnel junction device having a new structure, which may improve uniformity during the formation of the lower structure of the tunnel insulating layer, is required.
Typically, a single atomic material structure is used as a buffer or a crystalline material is used as a buffer, in order to realize perpendicular anisotropy in a magnetic material. As a result, grains having perpendicular anisotropy are formed to have a diameter of a few micrometers, and thus, in the case that a few tenths of nanometer-sized memory cells are formed in a spin transfer torque (STT)-magnetoresistive random access memory (MRAM) using perpendicular magnetic anisotropy, the possibility of obtaining defective cells may be increased when the cells are formed at grain boundaries.
Also, in a typical technique of controlling perpendicular magnetic anisotropy, the combination of a buffer layer matched with a lattice parameter and a crystal orientation of a material having perpendicular anisotropy is essential in order to control the perpendicular magnetic anisotropy.
However, in this case, a total thickness of the buffer layer increases due to the use of many buffer layers, a specific material having a matched crystal size may only be used, and limitations in processes may occur due to the use of many buffer layers.
Furthermore, deposition of the layer may be impossible on a material ordered in a L10 structure, such as FePt or FePd, which may be used as a pinned layer.